Render bacon in a heavy-bottomed skillet over medium-low heat.
Remove from pan with slotted spoon before fully crisp, but beginning to brown. Leave fat drippings in pan.
Add bay leaf, mustard seed, chili flakes, onions and salt and cook 10-12 minutes over medium-low heat, until onions are soft.
Add vinegar and stir to incorporate.
Mix in tomatoes and bacon.
Continue cooking over medium-low heat, or in a 350° oven, for 1 hour. The longer it cooks, the smoother the texture of the jam.
Fold in maple syrup.
Spoon jam into sterilized canning jars,
Press down the solids to push up air and fat.
The fat will cool and create a natural seal at the top.
Refrigerated, as long as the fat layer is on top, it should be good for an extended period of time.
Warm and serve over grilled steak or fish.